The chief tales are The Children of Hurin, in alliterative verse and The Lay of Leithian - Beren and Luthien, in rhyming octosyllabic couplets, epic, dramatic, poetry with insightful commentary.

Long Synopsis:

[from the book jacket]
This is the third volume of the History of Middle-earth, which comprises heretofore unpublished manuscripts that were written over a period of many years before Tolkien's Silmarillion was published. Volumes 1 and 2 were The Book of Lost Tales, Part One and The Book of Lost Tales, Part Two. Together, these volumes encompass an extraordinarily extensive body of material ornamenting and buttressing what must be the most fully realized world ever to spring from a single author's imagination.
"I write alliterative verse with pleasure," wrote J. R. R. Tolkien in 1955, "though I have published little beyond the fragments in The Lord of the Rings, except The Homecoming of Beorhtnoth." The first of the poems in The Lays of Beleriand is the previously unpublished Lay of the Children of Hurin, his early but most sustained work in the ancient English meter, intended to narrate on a grand scale the tragedy of Turin Turambar. It was left incomplete but includes a powerful account of the killing by Turin of his friend Beleg, as well as a unique description of the great redoubt of Nargothrond.
The Lay of the Children of Hurin was supplanted by the Lay of Leithian, "Release from Bondage," in which another major legend of the Elder Days received poetic form, in this case in rhyme. The chief source of the short prose tale of Beren and Luthien is The Silmarillion. This, too, was not completed, but the whole Quest of the Silmaril is told, and the poem breaks off only after the encounter with Morgoth in his subterranean fortress. Many years later, when The Lord of the Rings was finished, J. R. R. Tolkien returned to the Lay of Leithian and started on a new version, which is also given in this book.
Accompanying the poems are commentaries on the evolution of the history of the Elder Days, which was much developed during the years of the composition of the two Lays. Also included is the notable criticism in detail of the Lay of Leithian by C. S. Lewis, Tolkien's friend and colleague, who read the poem in 1929. By assuming that this poem is actually a fragment from a past lost in history, Lewis underlined the remarkable power of its author's imaginative talents and academic competence.
Before the Contents is a list of the accented words in the text with a key enabling braille readers to identify the specific accents.